Conventionally, a master vehicle is operated by an operator, a slave vehicle is an unmanned vehicle, the master vehicle and the slave vehicle have respectively control devices, the vehicles can be communicated with each other by radio, and a program is provided which enables the slave vehicle to travel in parallel to the master vehicle. An art in which the master vehicle and the slave vehicle have distance measurement devices and a distance between the master vehicle and the slave vehicle is adjusted to a predetermined distance.
An art in which a master vehicle and/or a slave vehicle have navigation devices such as GPS and positions of the master vehicle and/or the slave vehicle can be limited is known (for example, see the Patent Literature 1).